1. Field of the Invention
The present invention relates to a printed circuit board and a fuel cell using the same.
2. Description of the Background Art
Batteries that are small in size and have high capacitance are desired for mobile equipment such as cellular telephones. Therefore, fuel cells capable of providing high energy densities compared to conventional batteries such as lithium secondary batteries have been developed. Examples of the fuel cells include a direct methanol fuel cell.
In the direct methanol fuel cell, methanol is decomposed by a catalyst, forming hydrogen ions. The hydrogen ions are reacted with oxygen in the air to generate electrical power. In this case, chemical energy can be converted into electrical energy with extremely high efficiency, so that a significantly high energy density can be obtained.
A flexible printed circuit board (hereinafter abbreviated as an FPC board), for example, is provided within such a direct methanol fuel cell as a collector circuit (see JP 2004-200064 A, for example). Here, a configuration of the conventional fuel cell is described using FIG. 6. FIG. 6(a) is a plan view of the FPC board used in the conventional fuel cell, and FIG. 6(b) is a sectional view showing the configuration of the conventional fuel cell.
As shown in FIG. 6(a), a pair of conductor layers 52a, 52b is formed on one surface of the FPC board 51. In addition, extraction electrodes 53a, 53b are provided so as to extend out of the conductor layers 52a, 52b, respectively.
As shown in FIG. 6(b), a fuel cell 50 is constituted by the FPC board 51, a film electrode junction 54 and a housing 55. The film electrode junction 54 is composed of a polyelectrolyte film 54a, a fuel electrode 54b and an air electrode 54c. The fuel electrode 54b is formed on one surface of the polyelectrolyte film 54a, and the air electrode 54c is formed on the other surface of the polyelectrolyte film 54a. The housing 55 is composed of a pair of half portions 55a, 55b. The half portion 55a is provided with fuel passages 56 into which fuel (methanol) flows, and the half portion 55b is provided with air passages 57 into which air flows.
The FPC board 51 is bent with its one surface on which the conductor layers 52a, 52b are formed as an inner side. The film electrode junction 54 is sandwiched between the conductor layers 52a, 52b of the bent FPC board 51. Gaskets 58a, 58b are disposed in the periphery of the FPC board 51. Then, the half portions 55a, 55b of the housing 55 are attached so as to cover a portion, excluding the extraction electrodes 53a, 53b, of the FPC board 51 from both sides of the FPC board 51. Various types of external circuits such as electronic components are electrically connected to the extraction electrodes 53a, 53b that are exposed from the housing 55.
In this fuel cell 50, methanol is supplied to the fuel electrode 54b of the film electrode junction 54 through the fuel passages 56 of the half portion 55a. Moreover, air is supplied to the air electrode 54c of the film electrode junction 54 through the air passages 57 of the half portion 55b. In this case, methanol is decomposed into hydrogen ions and carbon dioxide by a catalyst to form electrons in the fuel electrode 54b. 
The hydrogen ions decomposed from the methanol pass through the polyelectrolyte film 54a to reach the air electrode 54c, and then react with oxygen in the air supplied to the air electrode 54c on the catalyst. Thus, the electrons are consumed while water is formed in the air electrode 54c. This causes the electrons to move between the conductor layers 52a, 52b of the FPC board 51 and supplies electrical power to the external circuits.
In the conventional FPC board 51 used in the fuel cell 50, the extraction electrode 53a is formed on its one end side and the extraction electrode 53b is formed on its other end side as described above. Therefore, the extraction electrodes 53a, 53b are arranged on different surfaces in a state where the FPC board 51 is bent. In this case, complicated operation of alignment is required when the external circuits are connected to the extraction electrodes 53a, 53b. In addition, reliability of connection between the external circuits and the extraction electrodes 53a, 53b is not sufficiently ensured, and problems such as a positional shift are generated.